Randomisation The randomization will be performed within each wave of the survey. The participants are given a unique identification number in the original study and this number will also be used for the present study. The first 3 digit in the identification number identifies the municipality of the participants and the last digit are given in the order the participants enters the original study. Within each wave of the study participants will be sorted according to their identification number and will be assigned a random number between 0 and 1. The investigators will use the Rand ('uniform') function in SAS to create the randomization sequence. If the numbers are less than 0.5 the participants will be allocated to control otherwise participants will be allocated to treatment.